问题
Currently, I am having a graphical issue with drawing small dots.
I notice that in most professional Calendar applications, the events calendar indentifier is a small dot whose color is the events calendar color.
I am current at the point of my application where I need to draw a BETTER dot. Heres a photo of what I mean.
It may not be noticeable here but the colored dot is pretty pixelated when its on my phone. I would like to remove the pixelation.
I went through a tutorial from Ray Wenderlich's website: Ray Wenderlich Core Graphics.
Here is what I got out of it for drawing the dot:
UIGraphicsBeginImageContext(cell.imageViewPic.bounds.size);
CGContextRef contextRef = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(contextRef, [[event calendar] CGColor]);
CGContextFillEllipseInRect(contextRef,(CGRectMake (0.f, 0.f, cell.imageViewPic.bounds.size.width, cell.imageViewPic.bounds.size.height)));
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
cell.imageViewPic.image = image;
So this actually implements the circle, but I added this to draw a small line around the circle to rid the pixelation but no go.
CGPoint startPoint = CGPointMake(cell.imageViewPic.frame.origin.x, cell.imageViewPic.frame.origin.y + cell.imageViewPic.frame.size.height - 1);
CGPoint endPoint = CGPointMake(cell.imageViewPic.frame.origin.x + cell.imageViewPic.frame.size.width - 1, cell.imageViewPic.frame.origin.y + cell.imageViewPic.frame.size.height - 1);
UIColor* color = [UIColor blackColor];
CGContextSaveGState(contextRef);
CGContextSetLineCap(contextRef, kCGLineCapSquare);
CGContextSetStrokeColorWithColor(contextRef, color.CGColor);
CGContextSetLineWidth(contextRef, 10.0);
CGContextMoveToPoint(contextRef, startPoint.x + 0.5, startPoint.y + 0.5);
CGContextAddLineToPoint(contextRef, endPoint.x + 0.5, endPoint.y + 0.5);
CGContextStrokePath(contextRef);
CGContextRestoreGState(contextRef);
All together looks like this...
UIGraphicsBeginImageContext(cell.imageViewPic.bounds.size);
CGContextRef contextRef = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(contextRef, [[event calendar] CGColor]);
CGContextFillEllipseInRect(contextRef,(CGRectMake (0.f, 0.f, cell.imageViewPic.bounds.size.width, cell.imageViewPic.bounds.size.height)));
CGPoint startPoint = CGPointMake(cell.imageViewPic.frame.origin.x, cell.imageViewPic.frame.origin.y + cell.imageViewPic.frame.size.height - 1);
CGPoint endPoint = CGPointMake(cell.imageViewPic.frame.origin.x + cell.imageViewPic.frame.size.width - 1, cell.imageViewPic.frame.origin.y + cell.imageViewPic.frame.size.height - 1);
UIColor* color = [UIColor blackColor];
CGContextSaveGState(contextRef);
CGContextSetLineCap(contextRef, kCGLineCapSquare);
CGContextSetStrokeColorWithColor(contextRef, color.CGColor);
CGContextSetLineWidth(contextRef, 10.0);
CGContextMoveToPoint(contextRef, startPoint.x + 0.5, startPoint.y + 0.5);
CGContextAddLineToPoint(contextRef, endPoint.x + 0.5, endPoint.y + 0.5);
CGContextStrokePath(contextRef);
CGContextRestoreGState(contextRef);
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
cell.imageViewPic.image = image;
The circle is still drawn but there is no "stroke" being drawn.
If anyone would give some pointers on how this pixelation issue is solved, please post!
回答1:
The pixelation is occurring because when you make the image context you don't take the screen scale into consideration. Your code should be something like this (note the 1st line):
UIGraphicsBeginImageContextWithOptions(cell.imageViewPic.bounds.size, NO, [UIScreen mainScreen].scale)
CGContextRef contextRef = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(contextRef, [[event calendar] CGColor]);
CGContextFillEllipseInRect(contextRef,(CGRectMake (0.f, 0.f, cell.imageViewPic.bounds.size.width, cell.imageViewPic.bounds.size.height)));
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
cell.imageViewPic.image = image;
Update: As someone commented, you can pass in 0 instead of [UIScreen mainScreen].scale. The docs agree:
The scale factor to apply to the bitmap. If you specify a value of 0.0, the scale factor is set to the scale factor of the device’s main screen.
回答2:
This is the same answer as @Christian Di Lorenzo.. But this is shorter at more straight forward.
Change This:
UIGraphicsBeginImageContext(cell.imageViewPic.bounds.size);
To this:
UIGraphicsBeginImageContextWithOptions(cell.imageViewPic.bounds.size, NO, [UIScreen mainScreen].scale);
来源：https://stackoverflow.com/questions/18725955/drawing-around-cgcontextref-to-remove-pixelation